Electrical pick-up



May 27, 1930. M. c. HOPKINS 1 1,760,647

ELECTRICAL PICK- UP FiledNo'v. 18, 1925 2 Sheets-Sheet 1 y 7, 1930. M. c. HOPKINS 1,760,647

ELECTRICAL PICK-UP Filed Nov. 8. H25 2 Sheets-Sheet 2 mm ////////////(1lh'/7//////////, L6

arrow dot Marcus fla akms Patented May 27, 1930 UNITED STATES PATENT OFFICE 1 MARCUS C. HOPKINS, OF WASHINGTON, DISTRICT OF COLUMBIA, ASSIGNOR TO HOP- KINS CORPORATION, OF NEW YORK, N. Y., A CORPORATIONyOF DELAWARE ELECTRICAL PICK-UT .Application filed November The present invention relates to the generation of alternating current, and aims to provide a device for transforming mechanical motion derived from a phonograph record into an alternating speech current suitable for amplification in aradio receiving set, or like apparatus, and ultimate reconversion into sound through loud speakers or annunciators.

This generator or pick-up is so designed 1 that it can be placed on the tone arm of a standard make of phonograph in place of the usual sound box, and will there convert into electrical pulsations the mechanical movements produced by a needle as it follows the groove of the phonograph record.

The present invention in its preferred form is characterized by having an armature which is damped or dead beat, and is free from chatter and pendulum effects. Great accuracy of reproduction is thereby attained.

This dampening of the a-rmature and freedom from chatter is brought about by careful phonetic insulation'of the pivot on Which the armature swings and by the use of rubher stops so positioned as to center the armature between the magnetic poles while at the same time permitting such movement as is essential to free passage of the needle. along the sinuous groove of the record.

The objects and advantages will become clear from the following detailed description taken in conjunction with the accompanying drawings wherein Fig. 1 is a perspective View of the pickup installed on the tone arm of a standard make of phonograph;

Fig. 2 is a fragmentary sectional view of the pick-up;

F ig. 3 shows the device partly in section as viewed from the upper end of the armature;

Fig. 4 is a diagrammatic representation-of the pole pieces, the armature, and the elec-' trical windings;

Fig. 5 is a longitudinal cross section, and.

Fig. 6 shows the structure as viewed from the left of Fig. 1.

In theembodiment' illustrated, the device comprises a collar 1 adapted to slip over and 60 frictionally engage the ent end 2 of apho- 18, 1925, Serial No. 69,807.

nograph tone arm of standard manufacture. Secured to this collar is a supporting plate 3 to one side of which is secured an insulating switch block 4 through which electrical connection conveniently may be established to the electrical conductors 5 and 6 leading from the generatingcoils of the device. The generator itself comprises a pair of fiat rectangular permanent magnets 7 and 8 spaced in parallel relation to one another with like poles opposite one another. A soft iron pole piece 9 of the shape shown schematically in Fig. 4 is bolted between one pair of like poles as shown in Fig. 3, anda similar polepiece lOlis bolted between the other pair of like p0 es.

The tapered extremities of these pole pieces form two strong magnetic fields wherein is positioned an armature 11 of Norway iron, the upper end of this armature lying in one field, and a lower portion lying in a-similar field. Midway between these two fields the armature is provided with a pivot 12 of hard drawn steel. This pivot is encased in a soft rubber tube 13 and does not touch or bear on any metal part. It is, therefore, phonetically insulated. I find that this is of importance in preventing chatter and the development of mechanical reactions which would distort the speech current.

The electrical windings in which current is generated by rocking movement of the armature on its pivot comprise a pair of coils 14 and 15 similarly wound and connected in series as shown in Fig. 4. Electrically speaking there is but a single winding, but for mechanical reasons and topermit easy assembly of the device, the coil is split into two parts, eachon its own spool. When the armature is in position within the coilsits enlarged ends 16 and 17 lie directly in the path of the magnetic flux passing from one pole piece to the other, and any rocking movement of the armature on its pivot will cause such a redistribution of the flux as to develop 21. voltage in the winding. The lower end of the armature is recessed to receive a phonograph needle 18. I prefer to use a relatively stiff needle, and to increase its stiffness there is threaded to the lower end of the armature a inn hard steel cap or clutch 19 which is so shaped as to grip the tapered face of the needle. A very rigid structure is thereby produced and the armature as a whole will follow with certainty the swinging movement of the needle point.

The armature is of such mass that it will not respond to frequencies less than sound frequencies. The structure as a whole is so designed that the needle may readlly follow the spiral groove of the phonograph record. As contributing in large measure to accurate re production of the sound recorded on the disc while at the same time excluding other and undesired movements of the armature, I make use of cushions so positioned as to keep the armature central.

Each of these cushions comprises an elongated plug 20 of soft rubber shaped like a sharpened lead pencil but smaller and fitting snugly in a hole drilled through a pole piece. An adjusting screw 21 threaded into an enlarged hole in the pole piece can be used to crowd this rubber plug forward until its sharply tapered end flattens out against the armature to form a small round knob or bead 22 (Fig. 2). There are four of these beads, one for each pole piece. Between the beads or cushions the armature can swing in response to sound frequencies while the pole pieces, because of their inertia and the inertia of the rigidly associated'parts remain relatively stationary. Nevertheless, the needle will follow the spiral groove of the phono graph record because a steady lateral thrust on the needle will be transmitted through a pair of the cushions to the pole piece, thereby swinging the tone arm of the phonograph on its pivot. In other words, the rubber cushions keep the armature in central position for sound reproduction while allowin for progression of the needle along the spiral of the record. The metal of the armature can not hit the metal of the pole piece but by a lateral thrust on the cushions at a frequency less than sound frequency will cause the pole piece to move with respect to the record. A striking of the armature on the pole piece would cause a rebound of a magnitude noticeable in the speech current just as impact of the armature pivot on solid metalwould cause a rebound or sound leakage that would be perceptible in the speech current. But by cushioning the armature on its swinging ends and cushioning the pivoton which it swings, no such extraneous influences are introduced into the speech current, and the armature is left free to reproduce in the form of generated current impulses the record of sound present on the phonograph record.

The pick-up is provided with a brass handle 24 by which it can be tilted back for replacement of the needle or to throw the needle out of action. This handle also serves to give to the structure such weight that the needle will bear on the record with about the same pressure as is customary in standard phonograph practice. A slightly heavier pressure is sometimes desirable.-

Alternating current thus generated as a speech current wherein the undulations correspond with the sound variations as recorded on the record can be amplified by the use of well known radio equipment. The output of this apparatus can be introduced into a radio receiving set in place of the pulsating current normally derived from the detector of the set. The amplitude of vibration can then be stepped up through the audio frequency stages of the radio set and the speech current thus amplified ultimately can be translated into sound through a loud speaker operated either with or without a power amplifier of well known construction.

Scratches and imperfections on the record are, as a rule, not transmitted because they are of the frequencies which the pick-up is designed to damp out. There is thus removed one incident of phonograph reproduction that has heretofore proved embarrassing.

Also I find that delicate tones which are not audible'in an ordinary phonograph can be taken from a phonograph record and, by this electrical method, can be regenerated or reproduced with very pleasing efl'ects. That is to say, phonograph records more faithfully record the original sounds than those records are usually credited with doing.

I claim:

1. In a device for generating speech current from a phonograph record, the combination of a pair of permanent magnets, opposing pole pieces clamped therebetween and spaced apart to form a pair of air gaps, an armature positioned in said air gaps, a pivotal support for said armature, cushioning members mounted on said pole ieces and engaging said armature at all times to position said armature when atrest and control its movement when in motion, means for supporting said ma nets on the tone arm of a phonograph, an means for operatively connecting said armature with a sound record.

2. In a device for generating speech current from a phono raph record, the combination of a pair of at rectangular permanent magnets, opposing pole pieces clamped therebetween and spaced apart to form a pair of like air gaps, an armature positioned in said air gaps, a cushioning pivotal support for said armature, cushioning members mounted on said pole ieces and engaging said armature at all tlmes to position said armature when at rest and control its movement when in motion, means for supporting said magnets on the tone arm of a phonogra h and a means for operatively connecting sai armature with a sound record.

3. In a device for generating speech current from a phonograph record, the combination of a pair of permanent magnets, two sets of opposing pole pieces clamped between said magnets and spaced apart to form a pair of air gaps, an elongated armature spanning said gaps, a pivot about which said armature oscillates in said gaps, resilient stops mounted on said pole pieces and serving to position said armature in said gaps when it is at rest and to control its inovementwhen it is in 1110- tion, means for supporting said magnets on the tone arm of a phonograph, and means for operatively connecting said armature. with a sound record.

4. In a device for generating speech current from a phonograph record, the combination of a pair of permanent magnets, two sets of opposing pole pieces clamped between said magnets and spaced apart to form a pair of air gaps, an elongated armature spanning said gaps, a pivot about which said armature oscillates in said gaps, said pivot being so located that vibration of said armature results in changes of gap length in each gap to change the total gap lengths between poles of opposite polarity in said air gaps, cushioning means mounted on said pole pieces and engaging said armature at all times to position said armature when at rest and control its movement when in motion, means for supporting said magnets on a tone arm of a phonograph, and means for operatively connecting said armature With a sound record.

In testimony whereof I afiix my signature.

MARCUS C. HOPKINS. 

